Nuclear reactor control rod with guide members



Oct. 22, 968 H. v. LICHTENBERGER 3,407,117

NUCLEAR REACTOR CONTROL ROD WITH GUIDE MEMBERS 2 Sheets-Sheet 1 FiledFeb. 15, 1967 JNVENTOR. F16 I HAROLD 1 1. ICHTENBERGER ATTORNEY diam/6Oct. 22, 1968 H. v. LICHTENBERGER 3,407,117

NUCLEAR REACTOR CONTRQL ROD WITH GUIDE MEMBERS Filed Feb. 15, 1967 2Sheets-Sheet 3 INVENTOR. HAROLD l/l/CHTENBERGER 1 A {baa ATTORNEY UnitedStates Patent 3,407,117 NUCLEAR REACTOR CONTROL ROD WITH GUIDE MEMBERSHarold V. Lichtenberger, West Simsbury, Conn., assignor to CombustionEngineering, Inc., Windsor, Conn., a corporation of DelawareContinuation-impart of application Ser. No. 493,512,

Oct. 6, 1965. This application Feb. 15, 1967, Ser.

14 Claims. (Cl. 176-86) ABSTRACT OF THE DISCLOSURE A control rodarrangement for a nuclear reactor with the rod being comprised oflongitudinally arranged tubes bonded together. interspersed among thetubes is a guide rod for contacting a guide member in the passage in thecore of the reactor which is to receive the control rod.

Description of the invention This is a contin-uation-in-part applicationof US. application Ser. No. 493,512, filed Oct. 6, 1965, now abandoned.

This invention relates generally to control rods as employed to controlthe reactivity in a nuclear reactor with the invention having particularrelation to such an improved control rod construction which lends itselfto simplified and more economic manufacturing than could be obtainedwith the designs heretofore utilized.

In accordance with the invention the control rod is comprised of one ormore flat members which, in effect, form blades with these flat membersbeing made up of a series of tubes having circular transverse sectionsand with the tubes being in side-by-side coplanar parallel relation. Thetubes are hermetically sealed by means of end caps which are welded tothe tubes and the tubes are formed into a rigid blade or member bybonding adjacent tubes together throughout their length. Suitable endfittings are provided at each end of the blade so as to provide aconnection for the blade with a control rod drive and a follower bladeif the latter is employed. The blades are formed or provided withrubbing rods which are coplanar with the blade and extend adjacent toand throughout the length of the blade, being bonded to the adjacenttube or tubes throughout the length of the blade. These rubbing rods mayhave a lateral dimension that is greater than the diameter of the tubesof which the blade is formed such that they project each side of thetubes and act as rubbing rods during manipulation of the control rod inthe control rod channel in the core of the reactor or, alternatively,the channel may be provided with guides or extensions directed inwardlyto engage these rods. The reactor core may be comprised of a pluralityof so-called fuel assemblies which are made up in general of parallelarranged fuel tubes with these tubes being in spaced relation. Atpredetermined locations in the assembly, in lieu of a fuel tube theremay be provided a guide rod which may be in the form of a tube ofsomewhat larger diameter than the fuel tubes such that this rod willextend laterally outward from the fuel assembly and into the channelprovided between adjacent assemblies for receipt of the control rod.This guide rod will then form the inwardly directed guide or extensionpreviously mentioned. With this guide arrangement, rubbing of the bladeagainst the portions of the core that form the control rod channelstakes place between the rubbing rods and not against the poisoncontaining tubular members of the control rod or the fuel containingportions of the core.

This control rod arrangement may be formed either in a single blade orin the well-known cruciform configura- 3,407,117 Patented Oct. 22, 1968tion. With this control rod structure commercially available tubes maybe employed for fabricating the same and by the use of these tubes,which have a circular cross section, excellent resistance to deformationfrom internal or external pressure is provided. It is essential that thetubes be joined together by an operation which will not distort thetubes so that accurate alignment of the tubes will be maintained.Ordinary welding would be unsatisfactory because of distortion andsoldering would be unsatisfactory because of the weakness of theresulting juncture. Therefore adjacent tubes are joined either bybrazing or by electron beam welding. The electron beam welding processadmits of very precise control with regard to the application of theelectron beam such that satisfactory results of joining the tubestogether is achieved without distortion of the tubes. The brazingprocess, of course, provides for uniform heating of the tubes and thusjoining them without distortion. The ends of the tubes may be welded inan ordinary fashion for the purpose of sealing the same, and the ends ofthe blades may be welded to the end fittings. These latter operationsmay be conducted without undesirable distortion. Furthermore, theseoperations are carried out prior to the joining of the tubes togetherand thus particularly in the brazing operation for thus joining thetubes. Any stresses caused by sealing the tube ends by welding will berelieved during this brazing operation.

While the tubes may be made of any suitable material which would becorrosive resistant and not subject to deformation because of radiationand which has suitable properties for which a suitable brazing materialis available or for electron beam welding, it is preferred that thetubes be fabricated of stainless steel or Inconel. The poison materialcontained within the tubes may be any of the known materials of highneutron absorption cross section used for controlling reactivity in areactor. One such preferred material is boron carbide.

Accordingly, it is an object of the present invention to provide animproved control rod for use with nuclear reactors.

Another object of the invention is to provide such an improved controlrod which is fabricated of corrosion resistant tubular memberscontaining therewithin a poison material with the members being joinedinto a rigid structure.

A still further object of the invention is to provide such a fabricatedcontrol rod which is relatively simple in construction such that it maybe economically produced and yet is highly reliable and satisfactory inits operation.

Other and further objects of the invention will become apparent to thoseskilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises anarrangement, construction and combination of the elements of theinventive organization in such a manner as to attain the resultsdesired, as hereinafter more particularly set forth by the followingdetailed description of an illustrative embodiment, said embodimentbeing shown by the accompanying drawings where- FIG. 1 is an elevationalview of the control rod of the invention;

FIG. 2 is a transverse sectional view of the control rod;

FIG. 3 is a fragmentary longitudinal sectional view of a portion of oneof the tubular members of which the control rod is comprised;

FIG. 4 is a fragmentary sectional view of a portion of modifiedembodiment of the invention.

Referring now to the drawings, wherein like reference characters areused throughout to designate like elements, the illustrative andpreferred embodiment of the invention depicted therein includes acontrol rod designated generally and which is of cruciform transverseconfiguration having two rows of tubes with these rows bcing identifiedas 12 and 14 in the FIG. 2 illustration and with each of these rows, ineffect, forming a blade with the blades being intersected as disclosed.The tubes of which the control rod are comprised are identified as 16and in each of the rows 12 and 14 these tubes are in parallel coplanargenerally tangent relation. The tubes are preferably of stainless steelor lnconcl although, as hereinbefore mentioned, other materials may beutilized. At the upper and lower end of the tube rows fittings 18 and 20are provided with these fittings being of the same material as thetubes.

Each of the tubes 16 has disposed therein a neutron absorbing material,such as 13 C with their being sufiicient space left within the tubes forthe accumulation of released gases that are produced during irradiationof the material as occurs during the operation of a reactor. This poisonmaterial may be in the form of a powder or in the form of slugs 22.After the material is disposed within a tube, the tube is welded closedat both ends with their being provided end caps 24 as disclosed in FIG 3and with these end caps being welded in place to hermetically seal thetube. The tube after thus being sealed is tested for leak tightness andthereafter the tubes are assembled in a suitable fixture which containsthe end fittings 18 and 20. In the arrangement of FIGS. 1 through 4there is also positioned in this fixture adjacent the endmost tubes ofeach row, or further down within the row if so desired, rubbing rods 26.These rods are coplanar with the row and have a thickness which isgreater than the diameter of the tubes 16 such that they protrude eachside of the row of tubes so as to act as a guide during insertion andremoval of the control rod in the core of the reactor. Any rubbing thatoccurs between the control rod and the reactor core will thus be againstthis rod and not the tubes 16. For instance, the tube 16 may have anoutside diameter of .165 inch while the rod 26 may have a thickness of.200 inch. This rod is formed of the same material as the tubes.

After assembling the tubes and these rubbing rods in the fixture, withthe tubes of each of the rows and the respective rods being in coplanartangent relation within this fixture, the tubes and rods are welded tothe end fittings and thereafter the assembly is bonded (by brazing orelectron beam welding) along the length of the tubes and at the juncturewith the end fittings to thereby form a rigid structure.

It will be understood that the control rod is received in a suitablepassageway 0r suitable passageways in the core of the reactor. This corewill have guide rods or guide means which will engage the rubbing rod 26to guide the insertion and removal of the control rod into and out ofthese passageways. Thus any rubbing action that takes place will bebetween these guiding elements of the core and the control rod and therewill not be rubbing of the fuel elements of the reactor core and thecontrol tubes of the control rod. The core is preferably comprised ofparallel fuel elements among which are disposed the guiding elements.

In the modified embodiment depicted in FIG. 5 rather than having therubbing rods of the control rod provided with a lateral dimensiongreater than the tubes of the control rod, the guides that form aportion of the core have a dimension such that they protrude somewhatinto the passageway within which the control rod is received. In thisillustrative organization of FIG. 5 there is depicted a portion of thecore of the reactor with there being a portion of four fuel assemblies28 being shown. These fuel assemblies are made up of fuel elements 30retained in a particular array with these elements containing a nuclearfuel. Between adjacent assemblies is formed the passageway 32 withinwhich is received the control rod hereinidentified generally at 35. Asin the previously described arrangement, this control rod is made up oftubes 16 and rubbing rods 26. The lateral dimension of these rods 26'may be the same as the diameter of the tubes 16. Positioned opposite therubbing rods 26 as they are disposed in the passageway 32 are guide rods34 which form part of the fuel assembly. These rods may, for example, besolid zirconium or stainless steel rods. They have a diameter somewhatgreater than the diameter of the fuel elements 32 such that they extendlaterally into the pars sageway 32 beyond the fuel elements such thatthese rods, together with the rubbing rods 26, provide a guiding actionfor guiding the control rod during its movement within the passage 32and without the fuel elements 30 and the control tubes 16 coming intorubbing engagement.

It is essential to this invention that the tubular members 16 be acircular transverse configuration. This is so in order to provide theresistance to deformation that will be encountered from both externaland internal pressure. Furthermore, with this tubing configurationwherein the tubes are tangent the bonding operation may be conducted ina very satisfactory manner without the production of voids or creviceswherein crevice corrosion may be produced.

With relation to prior art control rod design, the organization of thepresent invention has the following advantages:

(l) The control rod is a simple structure made up of parts which can bereadily fabricated and tested prior to assembly resulting in lessexpensive construction and greater structural integrity.

(2) The finished rod should be less susceptible to corrosion since itcontains no narrow passages or cracks for entrapment of foreignmaterials or has areas for crevice corrosion.

(3) Such control rods may be made with good dimen sional control sincethe distortion from welding is small and since the brazing operation(where employed) relieves the built-in stresses in the parts.

(4) The material exposed to the reactor coolant may be stainless steel,Inconel, or any other material having suitable properties for bonding bybrazing or electron beam welding.

While I have illustrated and described a preferred embodiment of myinvention it is to be understood that such is merely illustrative andnot restrictive and that variations and modifications may be madetherein without departing from the spirit and scope of my invention, Itherefore do not wish to be limited to the precise details set forth butdesire to avail myself of such changes as fall within the purview of myinvention.

What I claim is:

l. A control rod comprising in combination a plurality of parallel tubesin side-by-side relation, end fittings adjacent each end of said tubeswith said tubes being welded to said end fittings, said tubes having agenerally circular transverse configuration with there being disposed insaid tubes a poison occupying less than the entire volume of the tubes,adjacent tubes being bonded together throughout their length by anoperation that leaves the tubes generally without distortion, and rodmembers adjacent some of the tubes and bonded thereto by an operationthat leaves the tubes and rod members generally Without distortion, saidrods acting as a rubbing guide during manipulation of the control rod.

2. The control rod of claim 1 wherein said rod members have a thicknessgreater than the tube so as to protrude laterally each side of theadjacent tube.

3. The control rod of claim 1 wherein said tubes are brazed together andsaid rod members are brazed to said tubes.

4. The control rod of claim 1 wherein said tubes are joined together andsaid rod members are joined to said tubes by electron beam welding.

S. A control rod arrangement for a nuclear reactor comprising a corehaving passageways for receipt of control rods, a plurality of controlrod means for disposition within said passageways, at least some of saidcontrol rod means comprising a plurality of parallel tubes inside-byside relation, end fittings adjacent each end of said tubes withsaid tubes being welded to said end fittings, said tubes having agenerally circular transverse configuration with there being disposed insaid tubes a neutron poison occupying less than the entire volume of thetubes, adjacent tubes being bonded together throughout their length byan operation that leaves the tubes generally without distortion, rodmembers parallel with the tubes and bonded thereto by an operation thatleaves the tubes and rod members generally without distortion, said rodmembers acting as a rubbing guide during manipulation of the control rodmeans, and means extending inwardly of the passageway adjacent said rodmembers to engage the same for guiding the control rod means duringmanipulation.

6. The control rod arrangement of claim 5 wherein said tubes are brazedtogether and said rod members are brazed to said tubes.

7. The control rod of claim 5 wherein said tubes are joined together andsaid rod members are joined to said tubes by electron beam welding.

8. In combination a nuclear reactor core having a plurality of parallelfuel elements, said elements being arranged to provide a passageway forreceipt of a control rod, a control rod for insertion and removal intoand from said passageway, said rod being comprised of a plurality ofadjacent parallel tubes, said tubes containing a neutron poison, endfittings at each end of said tubes and welded thereto to effectivelyseal said tubes, said tubes having a generally circular transverseconfiguration with adjacent tubes being bonded together throughout theirlength by an operation that leaves the tubes generally withoutdistortion and with the tubes efiectively forming a blade, guide meansfor guiding the blade during its insertion and removal into and from thepassageway, said guide means including a rubbing rod disposed inparallel rela tion with the tubes and bonded to the tubes of the controlrod by an operation that leaves the tubes and rod members generallywithout distortion, and guide rods forming part of the reactor coredisposed at each side of the passageway and opposite Fil.lLl rubbing rodwhen the control rod is inserted in the passageway. said rubbing rod andguide rods being effective to guide the control rod and prevent thetubes of the control rod from contacting the fuel elements.

9. The organization of claim 8 wherein said passageways are formed byparallel fuel elements with these fuel elements being of circulartransverse section and wherein the guide rods are parallel with the fuelelements adjacent the passageways and are generally coplanar therewithwith these guide rods having a diameter greater than those of the fuelelements.

10. The organization of claim 8 wherein said guide rods protrude intothe passageway beyond the fuel elements which form the passageway.

11. The organization of claim 8 wherein said rubbing rods extendlaterally each side of the blade beyond the control rod tubes so as toengage the guide rods.

12. The combination of claim 8 wherein said tubes are brazed togetherand said rubbing rod is brazed to said tubes.

13. The control rod of claim 8 wherein said tubes are joined togetherand said rod members are joined to said tubes by electron beam welding.

14. A generally flat control rod blade comprising a plurality ofparallel coplanar tubes of circular transverse section, said tubes beinggenerally tangent and brazed together throughout their length, sealmembers welded to each end of the tubes to hermetically seal the same,the neutron poison material disposed within said tubes, said poisonmaterial occupying less than the full volume of said tubes, end fittingsadjacent each end of said tubes and welded thereto and rod membersparallel and coplanar with said tubes and brazed to said tubes so as toact as guides and rubbing rods during operation of the blade.

References Cited UNITED STATES PATENTS 2,861,035 11/1958 Zinn et al176-86 3,138,536 6/1964 Murrey et a] 17686 3,163,583 12/1964 Widmer etal 17686 3,194,743 7/1965 Deddens 176-86 CARL D. QUARFORTH, PrimaryExaminer.

H. E. BEHREND, Assistant Examiner.

